service unit
also: service file, .service unit, systemd service
A systemd unit file that defines how to start, stop, and manage a background service or daemon on a Linux system. Service units are configuration files with a .service extension that describe the executable, dependencies, and behavior of a long-running process.
A service unit is a systemd unit file (typically stored in /etc/systemd/system/ or /usr/lib/systemd/system/) that manages a daemon or background service. It contains metadata and instructions for systemd to control the service's lifecycle—starting, stopping, restarting, and monitoring it.
Service units use INI-style syntax and include sections like [Unit] (metadata), [Service] (execution details), and [Install] (installation targets). For example, a simple web server service might specify ExecStart=/usr/bin/nginx and Restart=always to restart the service if it crashes.
You manage services using systemctl commands: systemctl start myservice, systemctl enable myservice (auto-start on boot), or systemctl status myservice (check status). This replaces older init.d scripts with a unified, dependency-aware service management system.